I'm learning about 2D inviscid irrotational flows of constant density. In the example of flow past a cylinder there is the sentence "since the flow is irrotational as r tends to infinity, it is irrotational everywhere" and I can't get my hear around that. Why is this the case? Irrotational means that vorticity is zero, and in the case of an inviscid flow of constant density Kelvin's circulation theorem means that it remains zero as you follow any loop of fluid that initially has zero circulation. However I don't see why it is guaranteed that the flow is irrotational near the cylinder if it is irrotational at infinity. Thanks for any help!